A critical deficiency occurs in muscular development exercise machines of the prior art that impede an initial portion of an athlete's exercise stroke with a restraining force. This deficiency could lead to inadvertent serious damage to the athlete by strain or rupture of muscular tissue. The defect is that the restraining force magnitude could neither be accurately controlled, nor could it be controlled linearly over a vernier ranges of incremental adjustment that is critical in day-by-day exercise to improve muscular performance.
For example, in mechanical exercise machines of reasonable cost, it is difficult to hold tolerances close and precise. Even if this is done, after wear and subjection to impact forces that are involved in the subject exercise machines mechanical spacing adustments become unreliable in magnitude. Thus, even if an air gap is adjustable between a permanent magnet and magnetic member it the vicinity of the permanent magnet, a linear scale of vernier adjustment would not be feasible, since the magnetic forces are variable as the square of the distance between the magnetic members and known to be fixed distances cannot be established reliably.
Accordingly it is an objective of this invention to provide a safe, accurate vernier type control of the restraining force imposed upon the initial portion of an athlete's exercise stroke in an exercise machine.